"PSA" or "prostate-specific antigen" is a protein produced by the prostate gland and is found in the blood of males. When there is an abnormality with the prostate, it secretes more PSA. In the case of prostate cancer or even of inflammation of the prostate, more PSA is released into the blood. This higher level of the protein can be detected with a simple blood test. Since a spike in PSA does not always indicate prostate cancer, doctors will order further tests to determine the cause of elevated PSA levels.
Significance of PSA
PSA is the acronym for prostate-specific antigen, a protein produced by the prostate gland, found only in males. When the prostate gland detects something abnormal, such as inflammation or even the presence of cancer cells, it releases PSA into the bloodstream. This is why PSA is now known as a "marker" for prostate cancer, since it can be an early detector of the disease.
The Prostate Gland
The prostate gland, a walnut-size gland, which produces semen as well as PSA, is located under the bladder and surrounds the urethra. As men near 50, it is not uncommon for them to experience problems with urination, often caused by an enlarged prostate gland that puts pressure on the urethra thus preventing urine from draining easily from the bladder.
Tests for PSA Levels
To test the PSA level, phlebotomists draw blood from a vein in the arm and measure the PSA level. Cancerous prostate tissue usually secretes about 10 times as much PSA as normal prostate tissue does, so high levels of PSA in the blood normally indicate prostate cancer. PSA is measured in nanograms (ng), or billionths of a gram, per millilitre of blood.
Normal and Abnormal PSA Levels
PSA levels under 4 ng/ml are in the high-normal range. PSA levels of 10 ng/ml and above are in the abnormal range and usually indicate the presence of prostate cancer.
Causes of Elevated PSA Levels
There are several reasons other than the presence of cancer that can cause a PSA level to be elevated. If the patient has had a recent prostate biopsy or has an infection, his PSA level may appear high. Patients with benign prostatic hyperplasia (enlargement of the prostate in which the inner portion of the gland grows inward toward the urethra), a condition common in 20 per cent of men in their fifties and 70 per cent of men by age 70, often exhibit high PSA levels. Men who suffer from prostatitis, a painful condition of the prostate and often also the perineum (area between the testicles and rectum), also may well have high PSA levels.
Causes of Low PSA Levels
If a patient is on certain medications such as finasteride (Proscar TM or Avodart TM), prescribed for an enlarged prostate, his PSA level may appear low. A high-grade tumour of the prostate may also lower PSA levels, as the tumour is quite unlike normal prostate tissue and does not secrete PSA.
Accuracy of PSA in Cancer Detection
Like any indicator, PSA levels are not always 100 per cent accurate in detecting cancer. If a physician detects a slightly elevated PSA in a patient, he may wait and see if the level increases after the next year's test. Sometimes slightly elevated PSA levels indicate cancer, but biopsies of the prostate do not show the cancer until several years later. In a few cases, men will develop prostate cancer yet their PSA levels do not rise above normal. PSA doubling time or PSA velocity are both measurements of the rate that PSA levels rise. A shorter PSA doubling time or a rapid PSA velocity indicate a more aggressive type of prostate cancer, which will require a more aggressive treatment.